In UMTS (Universal Mobile Telecommunications Systems) systems, the wireless mobile telecommunication terminals are called upon to adjust their respective RF (Radio Frequency) output power to the momentarily required level. As a plurality of users share the same band frequencies within a cell of a UMTS system, one users communication signal is the origin of noise for the other communication signals of the respective other users. A power control is therefore necessary to keep the noise level down for the benefit of all users in a cell. In most cases, a mobile terminal is not required to transmit at its maximum RF output power. In the majority of cases, a transmission at lower power levels is sufficient. At these lower power levels the energy consuming high-power stage is typically turned off and bypassed. This saves battery power and increases the on air time of a mobile terminal.
A wireless mobile telecommunication terminal may be any user equipment like e.g. a mobile phone, a Personal Digital Assistant, a wireless remote enquiry measuring apparatus or the like. For convenience, a respective device mobile user equipment is briefly addressed as mobile terminal within the context of this specification.
An example of a respective bypass architecture of an RF power control on mobile terminals is given in EP 1 229 642 A1. The corresponding circuit diagram is shown in FIG. 1. The power amplifier is basically composed of an amplification path containing an RF power amplifier and a path bypassing the amplifier. In the high output power mode, an input RF signal is amplified by the amplification path, while the bypass will not influence the amplification. In low power mode, an RF input signal passes the circuit through the bypass path practically not affecting the signal power. The power supply to the power amplifier is turned off at the same time for reducing the average energy consumption.
The transmission (TX) circuitry of FIG. 1 allows only a coarse adaptation of the output RF power, i.e. outside a range provided by the amplification path itself. Further, switching between the amplification and the bypass mode results in a short mismatch of the circuit impedance which further causes a glitch in the RF output power. This in turn has a negative impact on the overall transmission conditions in a UMTS system.